The present invention relates generally to radio communication systems, and more particularly to a method and apparatus for encoding data for transmission in a radio communication system.
Radio communication systems rely on modulating carrier frequencies in a finite portion of the electromagnetic spectrum to wirelessly transmit and receive signals. Modulation can be performed on the amplitude, frequency, and/or phase of the carrier frequency to separate the signal from unwanted noise. The signals typically convey various types of information such as audio, video, and data to and from transceiving devices such as cellular base stations, cellular subscriber units, and personal computers.
In code division multiple access communication systems, a plurality of transmissions, each with its own code, can share the same band of frequencies. Each transmission is spread over the available bandwidth by mixing the signal to be transmitted with that signal""s unique code. For a CDMA system, spreading gain is defined as the ratio of chip rate to information data rate. This ratio also quantifies the redundancy for any particular user. Typically, information data stream is first encoded by a forward error correction (FEC) code such as a convolutional code. The FEC encoded data stream then is further spreaded by a code from an orthogonal codeword set.
In the forward link (the link from base station to the mobile station), prior art systems assign each user a single codeword from the orthogonal codeword set. By alternating transmission spreading between the assigned orthogonal code and its compliment, information is conveyed from a transmitter to a receiver. Since different transmitters use distinct codewords, the receiver can correlate the designated transmitter""s orthogonal code to retrieve its information and minimize interference.
Therefore, in the forward link, the orthogonal code has two functions, spreading and channelization. In spite of the large redundancy used by the spreading, this conventional orthogonal spreading/channelization does not provide any coding gains.
In accordance with a first aspect of the invention, a method for encoding data for transmission in a communication system, is provided. The method comprises the steps of partitioning a set of orthogonal codes into first and second subsets with a first and second number of members respectively, the second number of members being different than the first number of members. The method further comprises the step of partitioning first and second pluralities of data bits associated with first and second transmissions into first and second packets respectively. Still further, the method comprises encoding the first plurality of data bits by assigning each first packet to a corresponding member of the first subset and encoding the second plurality of data bits by assigning each second packet to a corresponding member of the second subset.
In some preferred embodiments, the communication system comprises a CDMA communication system. In other preferred embodiments, the first and/or second plurality of data bits represents an audio, video, and/or data signal. In still other preferred embodiments, the first plurality of data bits requires a lower power level than the second plurality of data bits and the first number of members is higher than the second number of members. In some embodiments, the first plurality of data bits requires a higher data rate than the second plurality of data bits and the first number of members is higher than the second number of members. In certain embodiments, the first plurality of data bits requires a lower error rate than the second plurality of data bits and the first number of members is higher than the second number of members.
In accordance with a further aspect of the present invention, a method for encoding data for transmission in a communication system is provided. The method comprises the step of partitioning a set of orthogonal codes into a subset with at least three members. The method further comprises the steps of partitioning a plurality of data bits into packets and encoding the plurality of data bits by assigning each packet to a corresponding member of the subset.
In accordance with another aspect of the present invention, a method for increasing the terminal capacity of a CDMA communication system is provided. The method comprises the step of providing a set of orthogonal codes. The method further comprises the steps of assigning at least three of the or thogonal codes in the set to a transmission and decreasing power associated with the transmission thereby increasing the number of transmissions capable of utilizing the CDMA communication system at a given time.
In accordance with yet another aspect of the present invention, a method for increasing the data capacity of a CDMA communication system is provided. The method comprises the step of providing a set of orthogonal codes. The method further comprises the steps of assigning at least three of the orthogonal codes in the set to a transmission and increasing a data rate associated with the transmission thereby increasing the amount of data transmitted by the CDMA communication system.
In accordance with still another aspect of the present invention, a method for decreasing the errors in a CDMA communication system is provided. The method comprises the step of providing a set of orthogonal codes. The method further comprises the steps of assigning at least three of the orthogonal codes in the set to a transmission and lengthening an error code associated with the transmission thereby decreasing the number of errors in the CDMA communication system.
In accordance with yet another aspect of the present invention, an apparatus for encoding a signal associated with a communication in a wireless communication system is provided. The apparatus comprises a memory storing a set of orthogonal codes. The apparatus further comprises a signal partitioner for partitioning the signal to be transmitted into packets having a number of members and a code partitioner for assigning a subset of the set of orthogonal codes to the communication, the subset including at least three codes. The apparatus also comprises an encoder for mapping the packets of the signal to the subset of the orthogonal codes.